This study aimed to validate the Revised Systems Thinking Measuring Instrument (Re-STMI) for high school and university students and examine the differences between the two groups. Data were collected from 475 high school students and 340 university students. Analyses were conducted using the Rating Scale Model of Item Response Theory and traditional Classical Test Theory methods including internal consistency reliability and independent-sample t-tests. The findings are as follows: First, the Rating Scale Model analysis indicated that students with higher levels of systems thinking were more likely to choose the highest score (5) for each item, and the item distribution exhibited a normal pattern around the mean item difficulty. Average systems thinking ability was higher among university students (1.21) than among high school students (0.94). Second, Differential Item Functioning (DIF) analysis showed that the items functioned equivalently across the two groups. Third, the internal consistency reliability of the instrument, based on Classical Test Theory, was high (Cronbach’s = .866). Additionally, the independent samples t-test revealed a statistically significant difference in the mean scores between the groups (p< .001). Based on these results, the instrument was verified to be valid through both Item Response Theory and Classical Test Theory frameworks. Therefore, the Re-STMI can be utilized in future research on systems thinking in various educational contexts.

Abstract
2. Research Method
    2.1. Research Procedures
    2.2. Research Instruments
    2.3. Research Subjects and Data Collection
    2.4. Data Analysis
3. Result
    3.1. Item Response Analysis-Rating Scale Model
    3.2. Validation of Group Differences BetweenHigh School and University Students: Cronbach’s, t-test, and Effect Size
4. Discussion and Conclusions
References

• Jaedon Jeon(Science Education Research Institute, Kyungpook National University, Daegu 41566, Korea)
• Hyundong Lee(Department of Science Education, Daegu National University of Education, Daegu 42411, Korea)
• Byung-Yeol Park(Institute of Integrated Science Education, Dankook University, Yongin 16890, Korea)
• Hyonyong Lee(Department of Earth Science Education, Kyungpook National University, Daegu 41566, Korea) Corresponding author